1. Field of the Invention
The present invention relates to an auto document feeder and a document reader arranged to read image information of a document while the auto document feeder is transporting the document.
2. Description of the Related Art
Conventionally, it is known that a document reader arranged to read image information of a document includes an auto document feeder. An auto document feeder is configured to separate stacked documents one by one to transport and guide each document to go through a position where image information of the document is read.
It is known that there are various configurations used in a document reader provided with an auto document feeder for reading both surfaces (a first surface and a second surface) of a document. For example, there is a configuration in which read units are included respectively for the first surface and for the second surface so as to read both surfaces through one-pass (one-pass type). In another example, there is a configuration in which a switch-back function is included to reverse a transport direction of the document (three-pass type). In addition to the above, there is another configuration in which a path for reversing front-back surfaces of the document is included and one read unit can read both surfaces of the document without using the switch-back function (two-pass type).
An auto document feeder of the two-pass type includes a lead path, a reverse path and an eject path. The lead path is an inverted U-shaped path which protrudes to one side and guides a document placed on a feed tray to a read position located below the feed tray. The document, which was guided to the read position and whose front page was read through the lead path, is then transported via the reverse path. The reverse path includes an inverted U-shaped path which protrudes to the other side and reverses the front-back surfaces of the document and guides the document back to the read position. The document, which was guided to the read position and whose second surface was read through the reverse path, is then transported via the eject path. The eject path, which includes a path which protrudes to the same direction (the one side) as the lead path, guides the document via a curve path smaller than the lead path to pass above the read position, and further guides the document above the reverse path to an eject tray.
In the above configuration, it is possible to read both surfaces of the document with one read unit without the switchback function.
However, the configuration of the two-pass type which can read both surfaces of a document through a path that reverses the front-back surfaces of the document generally has longer paths than those of other configurations, i.e. the one-pass type provided with two read units and the three-pass type provided with the switchback function.
Accordingly, it is necessary to include many transport rollers and transmission members and, as a result, the production cost increases. Further, in this configuration, the paths tend to be complicated and the paths are sometimes placed on top of each other.
For example, the auto document feeder of the two path type, on the left side of the read position, is arranged with the lead path and the eject path on top of each other (in parallel) on the one side. As a result, the size of the auto document feeder in the horizontal direction would be enlarged. Further, if a path near the read position is considerably curved, it may reduce the accuracy of the reading. In order not to reduce the accuracy of the reading, the curvature of the lead path and the eject path needs to be increased to a certain degree. However, if the curvature is increased, the paths would protrude to the one side, therefore making it difficult to reduce the size of the auto document feeder in the horizontal direction.